From e53dedac29b46904f7a3ba919079db8b97b72f57 Mon Sep 17 00:00:00 2001
From: Lewis Chung <lewis@withpersona.com>
Date: Wed, 25 Sep 2019 23:33:05 -0700
Subject: [PATCH] Add JSONLogic.uses_data to provide a means to find missing
 variables

---
 lib/json_logic.rb       | 16 ++++++++++++++++
 test/json_logic_test.rb | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/lib/json_logic.rb b/lib/json_logic.rb
index 914573e..d4eed59 100644
--- a/lib/json_logic.rb
+++ b/lib/json_logic.rb
@@ -16,6 +16,22 @@ def self.apply(logic, data)
     Operation.perform(operator, values, data || {})
   end
 
+  def self.uses_data(logic)
+    collection = []
+
+    operator, values = logic.first
+    values = [values] unless values.is_a?(Array)
+    if operator == 'var'
+      collection.append(values[0])
+    else
+      values.each { |val|
+        collection.concat(uses_data(val))
+      }
+    end
+
+    return collection.uniq
+  end
+
   def self.filter(logic, data)
     data.select { |d| apply(logic, d) }
   end
diff --git a/test/json_logic_test.rb b/test/json_logic_test.rb
index 72a913f..0d4d192 100644
--- a/test/json_logic_test.rb
+++ b/test/json_logic_test.rb
@@ -98,4 +98,37 @@ def test_in_with_variable
       { "x" => "foo", "y" => "bar" }
     )
   end
+
+  def test_uses_data
+    assert_equal ["x", "y"], JSONLogic.uses_data(
+      {
+        "in" => [
+          {"var" => "x"},
+          {"var" => "y"},
+        ]
+      }
+    )
+  end
+
+  def test_uses_data_missing
+    vars = JSONLogic.uses_data(
+      {
+        "in" => [
+          {"var" => "x"},
+          {"var" => "y"},
+        ]
+      }
+    )
+
+    provided_data_missing_y = {
+      x: 3,
+    }
+
+    provided_data_missing_x = {
+      y: 4,
+    }
+
+    assert_equal ["y"], JSONLogic.apply({"missing": [vars]}, provided_data_missing_y)
+    assert_equal ["x"], JSONLogic.apply({"missing": [vars]}, provided_data_missing_x)
+  end
 end